The results of experimental investigation into the design and geometry of resonant photoacoustic cells (Helmholtz resonator and differential Helmholtz resonator), as well as their sensitivity to gas pressure and modulation frequency of the exciting radiation are presented. A simple design of the Helmholtz resonator for flow measurements of absorption spectra and concentration of molecules is described. The characteristics of the resonant photoacoustic cells are theoretically analyzed based on the analogy with the electrical circuit approach. The test data for the designed photoacoustic cells with a CO2 laser and near IR diode laser are presented.